The present invention relates to an apparatus which controls the discharge of a molten material. More particularly, the present invention relates to a control device for controlling the discharge of molten material by means of a variable opening, formed between two cylinders with parallel axes. The cylinders are mounted between two symmetrical support blocks having bores. The boxes are spaced at a distance equal to the sum of their radii. Each bore includes a means for turning the cylinders in opposite directions around their respective axes. At least one of the cylinders has an external cut-out which, in conjunction with the surface of the other cylinders and upon rotation of the two cylinders, defines the variable opening. The present invention also includes two refractory lateral plates positioned at each end of the two cylinders. The present invention is particularly well suited for use in a continuous casting plant.
The present invention is preferably used to control the discharge of molten material, such as steel, aluminium and other metals. However its use is not limited to molten metals, and it may be used in other fields concerned with controlling the discharge of pyroplastic materials, such as the glass industry, the extrusion of plastics, and the like.
Continuous casting plants require a control means to start, stop, and regulate the rate of flow of metal during the casting operation. The control means is generally located between a molten metal reservoir and ingot molds lying below it. Control means presently used in industry involve systems of closure which use a plug or a slider. These systems work by enlarging or restricting the cross section of a discharge orifice by gradually removing or inserting an object, such as a stopper or a plate, between the opening and the molten metal to be cast. These systems affect the flow geometry of the molten metal and only work well in the open or closed positions. In the intermediate positions, the flow is severely disturbed, which adversely affects the quality of the casting operation.
Another prior art method for controlling the flow of molten metals is disclosed in document EP-A No. 1.0078 760. This control means prevents the severe disturbances caused by the slide or Plug control means discussed above. This method comprises two cylinders with parallel areas which have a common line of contact. The cylinders are moved around their respective axes. At least one of the cylinders includes a peripheral groove which extends over a portion of the surface of the cylinder. The groove has a perpendicular orientation to the axis and has a depth which progressively changes between a minimum and a maximum. When the grooved cylinders are in a side by side orientation, and the grooves are aligned in a symmetrical fashion so as to define an opening, a system is created wherein rotation of the cylinders in opposite directions achieves a progressive variation of the cross section of the opening. While the cross sectional area of the opening decreases, the general shape of the opening remains much the same as the initial cross section. While former control means progressively cut off the flow, the method of EP-A No. 1.0078 760 progressively throttles the flow. Despite the fact that this method has achieved substantial advances relative to previous methods, it is still imperfect. Unfortunately, leakage often occurs on either side of the grooves of the cylinders. Also, it is difficult to avoid lateral discharge of the molten metal. Moreover, another problem that exists with the grooved cylinder method is that because the cylinders by necessity, are made of refractory materials they are weak. Often, the torque exerted by the drive shafts exceed the strength of the cylinders resulting in a breakdown.